I'm not sure if the design of the small Keltec pistol has changed from the cock the hammer each time you pull design I have. I used to carry a Keltec 9mm that takes the S&W mags (1997/1998 vintage). I found it a reliable shooter, fairly accurate, if a little tougher to control than a large pistol.
I don't claim to be a KelTec historian, but I think you might have it confused with something else. KelTec has only made autos AFAIK and the only KT that i know of that takes S&W mag is the Sub 2000 rifle. Also the hammer on the PF-9, P32, and P3AT (and possibly the P-11) is completely shrouded by the slide and frame/grip.